Sustainable scale for energy use has been exceeded.Sustainable scale regarding energy use has to do with how much energy is being used in the global economy relative to how much is available and being renewed, as well as the impact of its use on critical ecosystem functions. Energy use is a scale problem from at least three perspectives:

Most of our energy is derived from non-renewable sources, and those resources will be depleted in the not too distant future (see Non-Renewables Are Unsustainable below)

The total amount of energy use is so great that it has the potential to disrupt global ecosystems by the sheer volume of material throughput resulting from energy use, regardless of the source (see The Downside of Energy Use).

Non-Renewables are Unsustainable

Our Dominant Energy Sources Are Non-Renewable

Sustainable scale of a resource that cannot be regenerated is zero, therefore sustainable scale is exceeded wherever energy is generated from non-renewable sources.Unfortunately, our energy consumption is depleting the earth’s reserves of non-renewable resources at a high rate.

Fossil fuels (coal, natural gas and oil) supply about 80% of global energy use, and the demand is growing at close to 2% per year.As non-renewable resources, their use is clearly unsustainable. While these resources will still exist in the ground for many years, both the financial and energy costs of bringing them to market will become increasingly prohibitive as their supplies dwindle.

Fossil Fuels: Unique But Vanishing Resources

The historical transition from wood to coal to oil and natural gas represented a significant increase in the ENERGY INTENSITY [glossary term] and flexibility of fuel sources.Oil is our highest quality fuel in terms of its energy content and flexibility, and has the highest energy intensity and energy return on energy invested (EROI) of any fuel. SWEET CRUDE [glossary term] has an EROI of 100:1, or some three to four times higher than wood.

Evidence is accumulating that oil will reach peak production globally in the current or next decade. When this occurs costs, in both financial and energy terms, will increase significantly as oil becomes more difficult to extract (www.peakoil.ie) .

At some point the EROI for oil will be negative.As peak oil is passed for individual conventional wells, more energy is required to extract it.As we increasingly rely even more on the use of less conventional petroleum sources (off shore, arctic areas, tar sands, etc), more energy is required to extract a barrel of oil.

The consequence is that EROI of oil for some producer nations has already declined considerably, to as low as 12:1.1This increase in the energy required to extract energy is much more serious than the expected increases in financial costs associated with peak oil production.Financial costs can be manipulated with subsidies and various economic mechanisms; energy costs depend on laws of nature and are immune to such manipulation.

Other Unique Features of Fossil Fuels

In addition to its high energy intensity and EROI, oil is also a uniquely flexible fuel, both in terms of its transportability and its uses.It can be transported at ambient temperatures in pipelines, ships, trains or trucks, and can be refined to make gasoline, kerosene, jet fuel, paraffin, asphalt, etc.

Petroleum is also the base for more than a thousand products from toothpaste and pharmaceuticals to fertilizers and pesticides.Once these resources are gone, we will have to find substitutes, if we can, to continue enjoying the non-energy products they provide.

Natural Gas: A Cleaner Fuel

Natural gas (methane) is far less polluting than either oil or coal, and increasingly has been substituting for them in residential, commercial and industrial sectors.Natural gas has many important uses such as heating, transportation, and as chemical feed stock. It can be transported through pipelines, but shipping natural gas is a hazardous process since it has to be shipped as a liquid at low temperatures (LNG).

LNG tanker facilities are very expensive and only available at a limited number of ports.Natural gas has less than half the CO2 emissions of coal for the same amount of energy, and is therefore preferable where ever it is feasible. Nevertheless natural gas is also a major contributor to global greenhouse gas emissions, and when released directly as methane has 40 times the global warming potential of CO2.

As with other fossil fuels, the EROI of natural gas is declining as less conventional sources must be tapped with the approaching onset of peak production. Natural gas is expected to reach peak production shortly after oil peaks, followed by coal, the most abundant fossil fuel, toward the end of the 21st century.

Coal: the Dirty Alternative

Coal is the most abundant fossil fuel; at present consumption levels and technologies, over 200 years of coal reserves are still available globally. If coal use is increased as a cheap replacement for oil, supplies will last for much less time.Coal is also the most polluting fossil fuel, emitting sulfur dioxide, nitrous oxide, carbon dioxide and particulate. The remaining coal is also of an inferior quality to what has been used to date.

Increased use of coal will produce large amounts of greenhouse gases, as well as contribute to acid rain, smog and local air pollution.Coal extraction often has huge local environmental impacts.

Attempts to clean coal, for example through coal liquification processes, do result in clearer combustion.However, they also greatly reduce the EROI for coal from 20:1 or more, to approximately 5:1.Long term dependence on coal is clearly not sustainable from both a source and sink perspective. If coal is used to bridge the needed transition to renewable energy sources, local and global ecosystems will be significantly degraded.

Nuclear Energy: A Similar Picture

Nuclear energy is not sustainable. Our current nuclear fission technologies are an uncertain substitute for fossil fuels, as supplies of fissionable materials are also limited. Currently, fission reactors provide only about 6 % of global energy needs.If more such reactors were to be built then known reserves of fuel for these reactors would be depleted in just a couple of decades.

Sources for nuclear fusion reactions are said to be “inexhaustible” but nuclear fusion is many decades away, at best, from commercial reality, and the remaining technical challenges are considerable.In addition, the EROI for nuclear fission reactors is considerably lower than that for fossil fuels (approximately 5:1).

Another important aspect of fossil fuel use from a scale perspective is the result of their combustion in terms of greenhouse gas emissions and their impact on climate change.As of 2004, atmospheric carbon dioxide, one of the most abundant greenhouse gases, exceeds the preindustrial level of CO2 by over 30%, and is projected to double or treble by the end of this century if present trends continue.

The atmosphere and oceans are not able to absorb more CO2 without significantly altering global climate patterns, resulting in a variety of global climate changes. Degradation of critical ecosystem functions such as climate stability threatens a variety of life support system upon which human civilization depends (see Climate Change

).

From a sink perspective, the amount of greenhouse gases emitted from fossil fuels (stimulated by economic growth and the consumption patterns of over six billion people) exceeds the regenerative capacities of critical global ecosystems (the global carbon cycle and naturally occurring greenhouse effect) to maintain global climate stability that has characterized virtually the entire period of human civilization. Whenever throughput is either non-renewable, or exceeds the regenerative capacity of ecosystems, sustainable scale is exceeded (see Understanding Scale).

Nuclear Energy:The Sink Side

Current fission technologies produce radioactive wastes that remain dangerous for thousands of years.Nuclear technologies without radioactive waste are a possible, but distant, option.To date no satisfactory method has been developed to safely dispose of the millions of tons of radioactive wastes already generated.

It is argued by some that a large number of nuclear power plants are needed to reduce the use of fossil fuels, as a bridge to renewables.These advocates of nuclear power often overlook the considerable amounts of fossil fuels that would be expended over the several years of construction of these plants; several years of subsequent operation are required before a net energy gain is generated. Fossil fuels used to build nuclear plants would therefore not be available for other uses, and this would occur over a period when petroleum is likely to be beyond peak production.From both a source and sink perspective, nuclear energy is unsustainable.

The Downside of Energy Use

Essential But Dangerous

Energy is required to do work; work involves moving matter through space over time.The more energy we use, the more matter we move.The more matter we move, the greater the impact on critical ecosystem functions.Sustainable scale on a macro level is about not moving more matter than critical ecosystem functions can tolerate – i.e. where the material throughput is less than the regenerative capacities of the ecosystems involved (see Critical Natural Capital, and Sustainable Or Unsustainable).

Having abundant clean energy could be a curse for humanity rather than a blessing.

Unprecedented Amounts of Energy Used

Energy is essential to our civilization.Energy is the largest sector of the global economy, and in turn drives all other sectors.Access to and use of energy is a major factor in determining the wealth of individual nations. Virtually everything we do requires energy of some sort, and our global commercial energy consumption is now over 10 GIGA TONES OF OIL EQUIVALENT [glossary term] annually.2On a per capita basis this is roughly equivalent to the work capacity of 20 human slaves for every person on the planet.

Current energy use has already disrupted a number of critical global ecosystems (see Areas of Concern), and has the potential to disrupt even more. Regardless of the source of energy used, continued or increasing levels of energy use are likely not compatible with maintaining critical ecosystem functions.

The key question of “how much is too much” is not being addressed by energy policy makers. Yet this question is extremely important to answer from a sustainable scale perspective as we approach a new phase in the evolution of a global regime of renewable energy sources.

Our Energy Options: Renewable Energy Sources

A Variety of Renewable Energy Sources Available

Transition to renewable energy sources is a necessary but not sufficient step (see The Downside of Energy Use), to achieve sustainable scale for energy. This conclusion derives from the following:

The unsustainable nature of the currently dominant fuels (oil, gas and coal)

the imminence of peak oil and natural gas over the next few decades

the climate consequences of continuing to use fossil fuels of any sort

the safety, supply, waste and EROI challenges of nuclear reactors

the expectation of a growing global demand for energy.

Fortunately, there are a variety of sources available to replace much of the energy now supplied by fossil and nuclear fuels.Each of these renewable energy sources has its own unique opportunities and challenges. It remains an open question as to whether it will be feasible for renewable energy sources to meet the level of demand anticipated, and whether from a sustainable scale perspective, such a level of energy use is desirable.

Sustainable Scale for Renewable Energy

Sustainable scale for renewable energy resources is currently unknown; we do not know how much energy could be generated from renewable sources without degrading critical ecosystem functions. At present, less than 20 % of global energy consumption uses renewable energy sources – hydro, biomass, solar, wind, geothermal, and ocean current and tidal (referred to as ocean thermal energy conversion, or OTEC).

Considerable technical, financial and environmental challenges must be overcome before any of these renewable sources could replace the energy output of fossil fuels, and none would be as flexible as petroleum. In addition, most renewable energy sources appear to have a low energy return on investment, or EROI.

Solar Energy

Solar energy is a primary renewable resource. How much of what reaches the earth is usable will depend on whether passive or active solar technologies are used; the efficiencies achieved by further research; and the infrastructure built to support it. The total amount of solar energy reaching the earth's surface is immense, but it is also dilute. Concentrating the dilute solar energy from the sun for human use itself requires energy; consequently the EROI for active solar technologies may be only 5:1 to 10:1.

Engineering studies have concluded that sufficient surface areas (e.g. on roof tops) are available in most industrialized countries to generate up to half of current electricity needs. But the amount of additional land that can be allocated for collecting solar energy will be competing with other land uses. Whatever amounts of solar energy are used to generate electricity will not be available to support the biosphere.

Human appropriation of photosynthesis is already over 40%, and will only increase as our population increases.Increased efficiencies for active solar technologies, such as photovoltaic cells, have recently been reported (some said to be more than 30% efficient).However, these increases may be leveling off, and further gains are questionable. In addition, life cycle analyses of photovoltaic cells indicate they have an ecological footprint equivalent to that of fossil fuels. Despite these drawbacks the price of photovoltaic units is becoming competitive with more traditional energy sources, and their use has been increasing rapidly in recent years as the price drops.

Wind Power

Wind power is perhaps the most promising source of renewable energy, and is one of the fastest growing alternatives.Efficiencies are improving. Use of wind turbines is in many cases compatible with agricultural land uses, although recent studies of large installations are finding changes in wind speed and increased transpiration, possibly affecting crop yields.

Wind turbines are also feasible offshore although these are more expensive to construct and maintain. Aesthetic concerns have been an obstacle in some areas, but wind is still growing globally at a rate of 30% annually.Wind has the potential to replace a large proportion of non-renewable fuels for electrical production in countries with adequate wind resources.

Some countries have made a major commitment to wind such as Spain, Germany, India, US, and Denmark.The main reason for the success of wind power is the decliningcost per KWH, making wind energy competitive in price with subsidized fossil and nuclear energy, and making wind a major future resource. Wind power’s EROI may be the highest of any renewable source, at 30:1 in favorable locations. The major drawback for wind is its variability between and within locations.

Hydro Power

New hydro electric dams are being built, often at great environmental and social costs, such as the 18,000 MW Three Gorges dam in China. Several major untapped river systems have the potential for generating additional power, but these are often in remote areas. Dams can also end up emitting considerable amounts of greenhouse gases. Much of the large scale hydro potential in developed countries has already been harnessed.

At the same time some older dams are being dismantled, largely for environmental reasons. Many of those that are still operating will eventually become nonfunctional due to siltation. The unprecedented task of refurbishing such large dams would require enormous financial, technical, material and energy resources. Opportunities for small scale hydro electric projects still exist. Large increases from this renewable source are unlikely. Large hydro is often classified as non-renewable due to the eventual siltation and decline in function of large dams.

Biomass Energy

Biomass is currently the most widely used renewable energy source. Wood, animal dung and crop waste are traditional biomass sources.New biomass sources include wood waste (converted to methanol), manure (converted to methane), and grains (converted to ethanol).

Care must be exercised in any expansion plans for biofuels. Dedicating forests or crop lands to biofuel production may compete with their increasingly important role in carbon sequestration, and the need for agricultural land to feed a growing global population. The latter will be especially important as soil fertility continues to decline, and as petroleum is less available as a source for chemical fertilizers.

Furthermore, the net gain in energy from biofuels can be small (often with an EROI of less than 2:1), depending on source and local environmental conditions. On the other hand, tree plantations may generate an energy return on investment as high as 40:1, as plantation growth and harvesting can be fairly efficient.

Geothermal PowerGeothermal power is abundant in the mantle of the earth, but is only near enough to the surface to provide large scale power in a very few locations around the globe, such as US, Philippines, El Salvador and Iceland. The EROI for geothermal power can vary widely depending on local conditions, and even where it is feasible there is a cooling effect over time.While some expansion of geothermal power can be expected, it is unlikely to be a major substitute for fossil fuels.

Tidal PowerTidal and wave sources of energy are in early stages of development and it is unclear at this point what future roles they might play in replacing fossil fuels. Tidal currents and tide levels are two different sources of tidal energy which are being developed.A new installation has recently been constructed on the Scottish coast generating approximatelyXX.

Fuel Cell Technologies

New fuel cell technologies are often touted as the answer to our need for clean energy.Of these, hydrogen fuel cell technologies are most developed.These cells can generate electricity and be used as stationary (e.g. for heating buildings) or mobile energy sources.

However, hydrogen is not itself an energy source but a carrier and itself requires energy to produce.How it is produced is an important issue in terms of sustainable scale.If hydrogen is produced by electrolysis and the electricity used is generated by a coal fired plant, serious environmental problems will continue and reliance on a non-renewable resource such as coal makes it unsustainable.

An innovative approach is being explored in Iceland where there is an abundance of geothermal power to generate clean electricity which can be used to extract hydrogen for fuel cells. But geothermal power is limited in scope, and there are many other technical problems to overcome before fuel cell technologies could conceivably provide a significant amount of energy.

There are several experimental projects where fuel cells are used to power buses and cars, but the technologies are not well enough advanced to become widely used.At best, widespread use is decades away.

The Future for Renewable Energy

Given the strengths and limitations of these various renewable energy sources, many knowledgeable analysts suggest that multiple sources will be the way of the future. However, each of these separate sources will require its own expensive infrastructure. The dismantling of current infrastructures, and in particular the development of new infrastructures, will themselves consume considerable amounts of materials and energy.

Furthermore, such infrastructure will take many years to design, develop and put in place. None of the renewables, however, have the flexibility of oil.Continuation of air transportation will be one of many large challenges for renewables.

It is impossible to identify the total amount of energy resources that might be available from renewable resources in 50 or 100 years. Research and development is in its early stages for several of these renewable energy technologies. And it is at least theoretically possible that new technologies could be discovered which radically increase efficiency.

But the amount of energy that can be generated from even renewable sources is finite, and some analysts have suggested that the growing global demand may not be met by these renewable sources once fossil fuels are exhausted.

Summary

A clear conclusion from these considerations is that civilization’s use of fossil fuels is not sustainable from either a source or sink perspective.The more desirable non-renewable resources (oil and gas) will be exhausted by the middle or end of the 21st century, depending upon demand and transition to renewable substitutes.

More importantly, the peak production periods for the more desirable fossil fuels (oil and gas) will begin very soon, leading to significant price increases. The renewable energy infrastructures required to replace them are not yet a priority for governments around the world.Continued use of fossil fuels will threaten global climate stability.

A more tentative conclusion of this brief review is that the global demand for energy may well exceed the amount that it is feasible or desirable to extract from renewable resources, in a timely, cost-effective or sustainable fashion. While technological innovations may continue increasing the efficiencies of renewable energy sources and applications, the total amounts of energy these sources can produce will be constrained by both biophysical and financial limits. These limitations have to do with both resource and sink limitations.

Nonetheless, the impact of various energy uses on ecosystems will be an ongoing concern (e.g. climate stability, ozone depletion, biodiversity loss, total material throughput, etc). Whether or not renewable energy sources will be sustainable at the level civilization demands will depend on the total level of demand made upon these resources and the specific technologies used to exploit them.

Increased energy use, even by renewables, may not be compatible with the scale of land, water, and other resource uses needed for manufacturing, installing, operating and disposing of these systems.Setting global priorities for energy use will become a major political issue, and we have not yet begun this discussion. (See Scale Relevant Solutionsfor some ideas about possible directions to sustainable scale for energy).